PROJECT SUMMARY Coronary heart disease (CHD) is a leading cause of death worldwide and it affects approximately two-thirds of patients with severe class IV heart failure, threatening more than 13 million Americans? life today. Although the traditional risks for CHD is well recognized, it is largely unknown how the genetic factors regulate the pathogenesis of CHD. In particular, it is unclear whether the mutations of the genetic factors have any negative impacts on the coronary vascular formation, and whether the malformed coronary vessels lead to susceptibility to CHD in human. T-box (Tbx) genes encode transcription factors (TFs) that play essential roles in a wide range of organs? development. Mutations in T-box genes are highly associated with human congenital diseases. We recently identified a previously unknown, specific Tbx2 expression in the coronary vessels. Through a series of newly generated mouse models, we found that mice with Tbx2 mutations do not form coronary vasculature properly, and mutants develop cardiac fibrosis with heart failure at adult stage. We further sequenced human patients with premature CHD, and identified TBX2 mutations on the same amino acid. These mutations lead to coronary artery smooth muscle cell growth arrest. Our overarching hypothesis is that Tbx2 transcriptional program plays central roles for coronary smooth muscle formation and function, and the mutated human TBX2 may result in malformed coronary vasculature. Our objectives are to apply genetic and biochemical approaches to study the biology of Tbx2, to gain comprehensive knowledge concerning how this critical TF regulates the downstream genes and govern coronary formation during gestation, whether Tbx2 genetic program is required for sustaining the coronary structure after birth, and whether the dysregulated Tbx2 transcriptional program leads malformed coronary vessels and susceptibility to CHD. In this program, we will characterize the genetic role of Tbx2 in the coronary vascular formation, and define the transcriptional network of Tbx2 in the coronary vessels. Our study will address central questions concerning coronary vascular development and disease.